1. Field of the Invention
The present invention relates to a charging device including a cleaning member configured to clean a grid electrode and a shutter configured to open/close an opening of a corona charger.
2. Description of the Related Art
Conventionally, there are known image forming apparatuses employing an electrophotographic method and using a corona charger in a charging process. Some corona chargers of such image forming apparatuses are known to have a grid electrode provided at an opening portion of a shield thereof to stabilize electric potential of a photosensitive member.
However, foreign matters, such as airborne toner particles, tend to accumulate on the discharge side of the grid electrode. When such foreign matters locally accumulate on the inner surface of the grid electrode, defective charging tends to occur at the portion corresponding to where the foreign matters have accumulated.
Japanese Patent Application Laid-Open No. 2005-338797 discusses a configuration that prevents foreign matters from accumulating locally on the grid electrode by providing a cleaning unit that cleans the inner surface (discharge wire side) of the grid electrode. To be more precise, while a cleaning brush as a cleaning member is in contact with the inner surface of the grid electrode, the cleaning brush is driven in the longitudinal direction of the grid electrode. In this manner, the inner surface of the grid electrode is cleaned.
The corona charger is known to generate corona products such as ozone (O3) and nitrogen oxide (NOX) when charging the photosensitive member.
When the corona products are attached to the photosensitive member, and the attached corona products absorb moisture, the surface resistance of a portion to which the corona products have attached is reduced. Under the condition where the corona products having absorbed moisture are attached to the photosensitive member, an electrostatic latent image which corresponds to the image information cannot be accurately formed, and a defective image called “image deletion” is generated.
To solve such a problem, Japanese Patent Application Laid-Open No. 2007-072212 discusses a configuration that includes a shutter for covering an opening of a corona charger, so that the occurrence of the image deletion is reduced.
In a state where the image formation is not performed (e.g., at nighttime or when the main body is powered off), the opening of the corona charger is covered. Before the image forming is performed, the closed shutter is opened. The user generally desires quick start-up of the image forming apparatus, thus requiring enhancement of the shutter-opening speed.
In the configuration where both the shutter and a grid cleaning member are driven in the longitudinal direction of the corona charger, it is desirable to use one drive source (motor) for driving both the shutter and the grid cleaning member, from the viewpoint of cost reduction.
However, in the configuration where one drive source is shared, when the shutter is quickly opened to reduce the start-up time, the moving speed of the cleaning member, which cleans the grid electrode, also increases. If a cleaning brush is used as the cleaning member, the fiber of the cleaning brush may be caught in the grid electrode when the cleaning brush moves quickly. In such a case, the fiber may be torn and fall off from the cleaning brush. Further, if the grid electrode is cleaned by a cleaning pad, the cleaning pad may wear out easily.
As described above, if the cleaning member is driven quickly and wears out, the cleaning of the grid electrode may not be performed to a satisfactory extent. As a result, the defective charging can be caused.